1. Field of the Invention
The present invention relates generally to measuring the period of square wave signals and, in particular, measuring the period of one pulse or the average of 8 pulses for use with frequency measurements.
2. Description of the Prior Art
A distance sensor, a conventional electromechanical transducer, usually mounts on a portion of a drivetrain of a vehicle and acts as a ground switch providing a series of on and off ground switch closures at a defined rate, e.g., 8,000 switch closures per mile traveled. 8,000 pulses per mile sensors usually emit 8 pulses per revolution of a sensor shaft. However, the pulses are not always outputted symmetrically as the sensor shaft rotates. This causes asymmetrical period readings of the sensor pulses. Also, the switch closures generate undesirable contact bounce. As much as 50 microseconds of bounce may result during the operation of an inexpensive, noisy distance pulse sensor.
In an effort to deal with the asymmetrical output pulses and the undesirable contact bounce characteristics of noisy sensors, a search was made to come up with a scheme to compensate for the asymmetry and the contact bounce characteristics. This search resulted in the present invention which measures the period of pulses outputted by the distance sensor.